Conducting polymers are a class of polymers which structurally feature a conjugated backbone and are electronically conductive. Some common conducting polymers are polyaniline, polypyrrole and polyacetylene. These materials are semi-conductors in their pure form. However, upon oxidation or reduction of the polymer, conductivity is increased. The oxidation or reduction leads to a charge imbalance which, in turn, results in a flow of ions into the material in order to balance charge. These ions or dopants enter the polymer from a surrounding, ionically conductive electrolyte medium. The electrolyte may be a gel, a solid, or a liquid. If ions are already present in the polymer when it is oxidized or reduced, they may exit the polymer.
In addition, it is well known that dimensional changes may be effectuated in certain conducting polymers by the mass transfer of ions into or out of the polymer. In some conducting polymers, the expansion is due to ion insertion between chains, whereas in others interchain repulsion is the dominant effect. Thus, the mass transfer of ions both into and out of the material leads to a contraction or expansion of the polymer. Typical volume changes are on the order of 10%, and linear dimensional changes are hence on the order of 3%. Stresses observed in current conducting polymer materials are on the order of 3 MPa.
Conducting polymer actuators are typically configured by immersion of the polymer in an environment of a bulk liquid electrolyte. Encapsulated conducting polymer actuators known in the art are limited to bilayers comprising multiple conducting polymer films in which a differential contraction and bending is induced.
Copending U.S. patent applications Ser. Nos. 09/130,500, filed Aug. 7, 1998, entitled "Conducting Polymer Driven Rotary Motor," 09/204,929, filed Dec. 3, 1998, entitled "Method of Manufacture of Polymer Transistors with Controllable Gap," and 09/263,980, filed Mar. 5, 1999, entitled "Conducting Polymer Generator-Actuator with Energy Storage/Recovery," disclose other applications for conducting polymers and are hereby incorporated herein by reference.